1. Field of the Invention
The present invention relates to a method and apparatus for improving the efficiency of heating systems, specifically heating systems that use a boiler to heat an energy transfer medium, such as a fluid, for circulation through heat exchangers in residential and commercial buildings. More specifically, the present invention relates to an automatic control of the boiler water target temperature for an improved hot water heating system with the object of enhancing energy efficiency during operation in diverse and varying temperature environments through the systematic reduction of the boiler target temperature predicated upon heating efficiency factors and external temperature conditions.
2. Description of Related Art
Hot water heating systems are closed-loop, fluid circulating systems that provide heat from an energy transfer medium, such as a fluid, and pump or circulate the energy transfer medium to an entire structure or zoned sections of a structure that requires a temperature increase greater than the external ambient temperature.
A boiler heating system operates by way of heating an energy transfer medium to a preset temperature and circulating that fluid throughout a building or structure typically through heat exchangers, such as radiators, baseboard heaters, or the like, to warm the structure or at least a portion of the structure. The fluid can be heated by any energy source, such as gas, or fuel oil, to name a few. The fluid is in an enclosed system and circulated throughout the structure within ingress and egress flow lines, such as conduits, usually by means of a motorized pump or circulator.
When there is a call or demand for heat, such as a low thermostat reading in a zoned space within a structure that has realized a drop in temperature and requires more heat, or a low thermostat reading within or near the boiler that registers a drop in transfer medium temperature due to a demand in usage, such as heating domestic hot water and having the temperature of the energy transfer medium decline as a result, a burner is fired within the boiler to heat the energy transfer medium until the call for heat is removed or a predetermined boiler transfer medium temperature is reached, whichever comes first. The zoned spaces are responsive to changing ambient weather conditions in that there occurs continuously heat exchange between these zones and prevailing ambient weather conditions. Once the demand for heat is satisfied, the demand is removed, and the heating cycle repeats.
The efficiency of a boiler can be directly affected by the change in temperature of the outside environment. The ideal situation is to establish a lower boiler water temperature in warmer weather when the boiler is in less demand, and higher boiler water temperature in colder weather, when the demand is high, dependent in part upon the thermal efficiency of the space being heated. A higher temperature heat delivery system will provide heat to a space more quickly, but is less efficient during warmer ambient conditions insomuch as the burner fires for longer periods of time or more often to keep the boiler water temperature unnecessarily high.
With energy efficiency becoming of paramount importance, it is desirable to have a hot water heating system that can automatically adjust to changing ambient conditions in a manner that allows the boiler to operate more efficiently.
Furthermore, the widely accepted technology of an outdoor reset control requires the installation of a temperature sensor outside, typically to a Northern exposure location. Installation of this system is labor-intensive and time consuming. Moreover, building constraints will affect structural placement of the outdoor reset control system. Additionally, without explicit building information, outdoor reset controls are typically conservatively set, resulting in a less efficient operation.
Many prior art attempts have been made to control a heating system and make the heating system more efficient by optimizing the heating cycle. In many circumstances, control circuitry and logic dictate the use of lower temperature boiler water for milder ambient weather than that used or required under colder and more severe weather conditions. These systems are uniquely different in that the methods for making a boiler responsive to repetitive or prolonged calls or demands for heat employ different algorithms and logic, all differing in implementation and having various degrees of complexity.
For example, in U.S. Pat. No. 6,402,043, issued to Cockerill on Jun. 11, 2002, entitled “METHOD FOR CONTROLLING HVAC UNITS,” the temperature set point of an HVAC unit is adjusted using two sensors. One sensor monitors the thermostat in a controlled environment, and a second sensor measures the temperature of the energy transfer medium. An ideal HVAC demand model is created for the controlled environment. The first sensor reads thermostat activity at set intervals over a defined period of time. At the conclusion of the defined time period, a microprocessor creates an actual demand model based on the recorded thermostat activity. The actual HVAC demand model is then compared to the ideal HVAC demand model. A temperature change factor is calculated from the comparison. An optimum temperature set point for the HVAC unit is then determined. The microprocessor adjusts the actual temperature set point of the HVAC unit to the optimum temperature set point. The HVAC unit is then activated whenever the temperature of the energy transfer medium deviates from the temperature set point by more than a predetermined set point range. The efficiency of this system is dependent upon the accuracy of the ideal demand model created for a given structure.
In U.S. Pat. No. 6,409,090, issued to Gilvar, et al., on Jun. 25, 2002, entitled “SELF-OPTIMIZING DEVICE FOR CONTROLLING A HEATING SYSTEM,” the heating unit has an ON state initiated when a measurable variable of the heating medium, such as a temperature reading, reaches a maximum level. Once the heating unit is signaled ON, a timer measures the length of time from initiation of the OFF state of the heating element until the temperature of the heating medium decreases below a predetermined minimum level. A processor then determines a delay time which delays the initiation of the next ON state by the delay time amount. This is distinctly different from systems that do not use a delayed initiation.
In contrast to reducing the temperature of the energy transfer medium, in U.S. Pat. No. 4,433,810, issued to Gottlieb on Feb. 28, 1984, entitled “HOT WATER HEATING SYSTEM,” operation of the heat exchange medium's circulating pump is controlled. Control circuitry connects to both the circulating pump and the boiler and works to lower the boiler operating temperature when detecting a significantly longer period of non-operation of the pump than a period of operation for a given selected period of time. For a predetermined time interval, the operation and non-operation of the pump is monitored. If the pump is non-operational during this time period, this signifies that for the prevailing ambient weather conditions the temperature level of the hot water being circulated through the heat system is unnecessarily high. In these instances, where the pump has only nominal operation, the operating temperature level of the boiler is lowered because the exchange medium is running too hot. Importantly, it is the operation and non-operation of the circulating pump that governs the temperature control. A consequence of the reduction in temperature of the heat exchange medium is that the circulating pump will remain ON for a longer period of time than prior to the temperature reduction. In this manner, a continuously running pump represents an optimum condition. In comparison, the present invention reduces the boiler target temperature on a demand for heat, and not simply for a period of time of non-operation of the circulator pump.
In U.S. Pat. No. 5,692,676, issued to Walker on Dec. 2, 1997, entitled “METHOD AND APPARATUS FOR SAVING ENERGY IN CIRCULATING HOT WATER HEATING SYSTEMS,” a method is taught for automatically adjusting the temperature of the boiler water in a hot water heating system in proportion to changes in the heat demand rate in the space being heated, wherein the change in heat demand rate is specifically established on the basis of the off-time interval in the cyclic OFF and ON activation of the pump which circulates the water.